The present invention relates to a method and apparatus for testing the electrical characteristics of an electronic element (object to be tested).
In particular, the present invention relates to a method and apparatus for testing the electrical characteristics of an electronic element having an electrode with which a measurement contactor comes into electric contact and, more specifically, to a method and apparatus for testing the electrical characteristics of integrated circuits formed on a semiconductor wafer (to be merely referred to as a "wafer" hereinafter) and of integrated circuits individually diced off from a wafer.
A case will be described in which the present invention is applied to a method and apparatus for testing an integrated circuit formed on a wafer. The present invention relates to a method and apparatus for testing the electrical characteristics of all the electronic elements (objects to be tested) each having an electrode with which a measurement contactor comes into electrical contact. Accordingly, the present invention is not limited to a method and apparatus applied to a method and apparatus for testing an integrated circuit formed on a semiconductor wafer.
In a semiconductor manufacturing process, various steps, e.g., a step of forming a thin film on a wafer by thermal CVD, plasma CVD, or the like, an etching step of removing any unwanted thin-film portion on the wafer, and the like are performed to form a large number of integrated circuits on the wafer. Thereafter, these integrated circuits are diced into individual IC chips and are packaged. Before this packaging, a testing step of testing the electrical characteristics of the respective integrated circuits on the wafer and screening non-defective/defective integrated circuits is run. Alternatively, the same test step is run for the individual IC chips diced off from the wafer.
For example, a probe device is used for this testing step. The probe device generally has a loader unit and a prober unit adjacent to it. The loader unit is a section that conveys the wafer to the prober unit, and has tweezers for conveying one by one wafers stored in a cassette, and a sub chuck for prealigning the wafers during conveyance with the tweezers. The prober unit is a section that electrically tests the wafers. The prober unit has a main chuck and a probe card. The main chuck places the wafer on it, and moves the wafer in the X, Y, and .theta. directions to align the wafer. The probe card has measurement contactors (probe needles) that come into electrical contact with the electrode pads (made of, e.g., aluminum) of the respective integrated circuits of the wafer on the main chuck, and exchange an electric signal with a tester. In testing, the loader unit extracts a wafer from the cassette with the tweezers and sends it to the prober unit. During this conveyance, the sub chuck prealigns the wafer. After the prealignment, the wafer is moved to the main chuck of the prober unit with the tweezers again. In the prober unit, the main chuck moves in the X, Y, and .theta. directions to align the wafer. After the alignment, the main chuck moves upward in the Z direction (vertical direction). The probe needles of the probe card come into electrical contact with the electrode pads of the wafer. An electrical signal is exchanged between the tester and the integrated circuits to run a predetermined test on the electrical characteristics. After the test, the wafer is returned into the cassette following the procedure opposite to that described above. Thereafter, the same operation is repeated to test the electrical characteristics of all the wafers in the cassette.
Concerning the integrated circuit on the wafer, as shown in FIG. 5, FIG. 6 and FIG. 7 as well, a wiring layer or interconnect L made of a conductive metal, e.g., aluminum, is protected by a passivation film I made of a polyimide-based resin or the like, and an electrode pad P formed in part of the wiring layer L is exposed from the passivation film I. The aluminum of the exposed electrode pad is extremely prone to oxidation. The surface of this aluminum forms a hard oxide film O having a large thickness (e.g., several 100 .ANG.) due to heat that acts when the passivation film I is formed. Alternatively, a natural oxide film O having a small thickness (e.g., several 10 .ANG.) is formed on the surface of this aluminum by natural oxidization during wafer conveyance. The oxide film O is an insulator and increases the electrical contact resistance in contact of the probe needle with the electrode. When testing the integrated circuit, if the electrode pad P and the contactor merely come into contact with each other, the resistance of the conduction line between them is increased by the oxide film, making it difficult to perform accurate measurement.
When testing a wafer, the film on the electrode pad must be removed, and thereafter the probe needle must be brought into contact with the electrode pad. For this purpose, if, for example, an oblique probe needle is used as the contactor of the probe card, the main chuck (not shown) on which the wafer is placed is overdriven in the Z direction, as indicated by an arrow Z in FIG. 5. By this operation, the needle point of a probe needle N moves in the direction of an arrow Y to shave the oxide film O of the electrode pad P. Then, the probe needle N is brought into direct contact with the electrode pad P to test the integrated circuit. When a vertical needle N1 is used as the contact of the probe card, as shown in FIG. 6, or when a membrane probe card is used as the probe card and a bump N2 is used as the measurement contactor, as shown in FIG. 7, the main chuck is overdriven in the Z direction, as indicated by an arrow Z in FIG. 6 and FIG. 7, and is moved in the Y direction. By this operation, the needle point of the vertical needle N1 of the probe card or the bump N2 of the membrane card shaves an oxide film O. Thus, the vertical needle N1 or bump N2 is brought into direct contact with the electrode pad P to test the integrated circuit.
As described above, conventionally, when the object to be tested is tested by causing a measurement contactor (e.g., a probe needle) to come into contact with the electrode pad P of the integrated circuit formed on the wafer, the film (e.g., an insulating oxide film) on the electrode pad that increases the electrical contact resistance must be removed. For this purpose, the main chuck on which a wafer W is placed is overdriven, or the main chuck is moved upward and simultaneously vibrated slightly in the horizontal direction to shave the insulating oxide film (aluminum oxide film) on the electrode pad P. This conventional testing includes problems as follows.
While the insulating oxide film (aluminum oxide film) on the electrode pad P with the probe needle N is shaved repeatedly, the probe needle N deforms. The heights of the needle points of the large number of probe needles N accordingly become non-uniform, the positions of the needle points are displaced, and contact of the probe needles N with the electrode pads P becomes unstable. As a result, stable measurement cannot be performed, and the service life of the probe needles N suffers.
The shaving of the insulating oxide film (aluminum oxide) attaches to the needle points of the probe needles to make contact of the probe needle N with the electrode pad P unstable, making it difficult to run stable testing. Also, an additional operation of removing the shaving attaching to the probe needle becomes required.
The complicated operation of overdriving the main chuck and the like requires a complicated, sophisticated control system.
If a probe needle comes into contact with a portion, where the insulating oxide film of the electrode pad P is not shaved yet even with the shaving operation described above, and performs measurement, accurate measurement cannot be expected.